Narrative:

The airfield was dark and all airfield lighting was operational. I was training on local control (combined with ground control; for which I am already rated) with my instructor; and the controller in charge was working the clearance delivery position. I was responsible for three aircraft at the time: an erj; a twin cessna; and a C172. Twin cessna was cleared to land on runway 28. Shortly afterward; the erj was cleared for take-off and informed of the twin cessna on final. Just prior to this; C172 called for taxi instructions. I told him to; 'taxi to runway 28 via alpha and charlie; cross runway 10.' he replied that he needed help getting to the runway. I replied to him that he needed to; 'make a left onto alpha; then the next right onto charlie; and cross runway 10.' the pilot read back the instructions correctly. I continued my scan and watched all three aircraft simultaneously.as C172 neared the alpha and charlie intersection; I had trouble telling if he was indeed going to make the right turn onto charlie; so I picked up my binoculars to verify that he was doing what I had instructed him to do. At this time; I could tell he had missed the turn for charlie; and was about to incur onto runway 28; on which erj was well established on takeoff roll and nearing the runway intersection just east on C172's position. I immediately told C172 to; 'stop! Hold position! You need to make a right turn onto charlie!' C172 responded by saying; 'wait...oh!' immediately after this; my instructor and I; as well as the controller in charge; observed that he had already crossed runway 28 and was just clearing the runway. I would estimate the time between when C172 cleared the active runway and then erj crossed the runway 28/alpha intersection to be about 2 or 3 seconds. In the future; I think I will be much more careful with pilots who are unfamiliar (or who I think may be unfamiliar) with the airport. Rather than give him the whole route; it would have been better to give him just one piece of taxi instructions at a time (strictly progressive taxi). In the future; I will make sure to use this method; especially at night. I will also devote even more time from my scan to aircraft which seem unsure of what they are doing. Additionally; I am going to review JO7110.65; in reference to progressive taxi instructions; to ensure that I can provide low-time and unfamiliar pilots with the best possible taxi instructions. I would recommend; however; that the airport authority make sure that the taxiway markings in the vicinity of taxiways alpha and charlie; as well as all runways; are fully lit and easily seen.

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Original NASA ASRS Text

Title: SAV Controller described a runway incursion event when traffic taxiing failed to follow taxi route instructions; the reporter noting more detailed and progressive taxi instructions may have prevented this occurrence.

Narrative: The airfield was dark and all airfield lighting was operational. I was training on Local Control (combined with Ground Control; for which I am already rated) with my instructor; and the CIC was working the Clearance Delivery position. I was responsible for three aircraft at the time: an ERJ; a twin Cessna; and a C172. Twin Cessna was cleared to land on Runway 28. Shortly afterward; the ERJ was cleared for take-off and informed of the twin Cessna on final. Just prior to this; C172 called for taxi instructions. I told him to; 'taxi to Runway 28 via Alpha and Charlie; cross Runway 10.' He replied that he needed help getting to the runway. I replied to him that he needed to; 'make a left onto Alpha; then the next right onto Charlie; and cross Runway 10.' The pilot read back the instructions correctly. I continued my scan and watched all three aircraft simultaneously.As C172 neared the Alpha and Charlie intersection; I had trouble telling if he was indeed going to make the right turn onto Charlie; so I picked up my binoculars to verify that he was doing what I had instructed him to do. At this time; I could tell he had missed the turn for Charlie; and was about to incur onto Runway 28; on which ERJ was well established on takeoff roll and nearing the runway intersection just east on C172's position. I immediately told C172 to; 'Stop! Hold position! You need to make a right turn onto Charlie!' C172 responded by saying; 'Wait...oh!' Immediately after this; my instructor and I; as well as the CIC; observed that he had already crossed Runway 28 and was just clearing the runway. I would estimate the time between when C172 cleared the active runway and then ERJ crossed the Runway 28/Alpha intersection to be about 2 or 3 seconds. In the future; I think I will be much more careful with pilots who are unfamiliar (or who I think may be unfamiliar) with the airport. Rather than give him the whole route; it would have been better to give him just one piece of taxi instructions at a time (strictly progressive taxi). In the future; I will make sure to use this method; especially at night. I will also devote even more time from my scan to aircraft which seem unsure of what they are doing. Additionally; I am going to review JO7110.65; in reference to progressive taxi instructions; to ensure that I can provide low-time and unfamiliar pilots with the best possible taxi instructions. I would recommend; however; that the Airport Authority make sure that the taxiway markings in the vicinity of Taxiways Alpha and Charlie; as well as all runways; are fully lit and easily seen.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.